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TUNED CIRCUIT—(1) A circuit consisting of inductance and capacitance that can be adjusted for
resonance at a desired frequency [9]. (2) A circuit that is used as a filter which passes or rejects specific
frequecies [16]. (3) An LC circuit used as a frequency-determining device [8].
TUNED LINE—Another name for the resonant line. This line uses tuning devices to eliminate the
reactance and transfer maximum power from the source to the line [10].
TUNNEL DIODE—A heavily doped semiconductor device that has high gain and fast switching
capabilities [7]. See NEGATIVE-RESISTANCE ELEMENT [11].
TUNNELING—The piercing of a potential barrier in a semiconductor by a particle (current carrier) that
does not have sufficient energy to go over the barrier [11].
TURN—One complete loop of a conductor about a core [2].
TURNS RATIO—The ratio of the number of turns in the primary winding to the number of turns in the
secondary winding of a transformer [2].
TURNSTILE ANTENNA—A type of antenna used in vhf communications that is omnidirectional and
consists of two horizontal half-wave antennas mounted at right angles to each other in the horizontal
plane [10].
TWISTED PAIR—A line consisting of two insulated wires twisted together to form a flexible line without
the use of spacers [10].
TWO-DIMENSIONAL RADAR (2D)—Measures the range and bearing to a target [18].
TWO-M (2M)—Miniature/microminiature repair program [14].
TWO-WIRE OPEN LINE—A parallel line consisting of two wires that are generally spaced from 2 to 6
inches apart by insulating spacers [10].
TWO-WIRE RIBBON (TWIN LEAD)—A parallel two-wire line in which uniform spacing is assured by
two wires imbedded in a low-loss dielectric [10].
ULTRAHIGH FREQUENCY—The band of frequencies from 300 megahertz to 3 gigahertz [17].
ULTRASONIC—(1) Sounds above 20,000 hertz [10]. (2) Supersonic.
UNBALANCED CRYSTAL MIXER—A circuit consisting of a section of coaxial transmission line
one-half wavelength long that is tuned to the difference (intermediate) frequency between the local
oscillator and RF echo signals [18].
UNIDIRECTIONAL—In one direction only [1].
UNIDIRECTIONAL ARRAY—An antenna array that radiates in only one general direction [10].
UNIJUNCTION TRANSISTOR (UJT)—A three-terminal, semiconductor device with a negative
resistance characteristic that is used in switching circuits, oscillators, and wave-shaping circuits [7].
UNIT—(1) An assembly or any combination of parts, subassemblies, and assemblies mounted together.
Normally capable of independent operation [17]. (2) A single object or thing [13].
UNIT SIZE—The standards adopted to make comparisons between things of like value (for example, the
unit size for conductors is the mil-foot) [4].
